Today's KNOWLEDGE Share : Mainstream Polyester Production Processes

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Today's KNOWLEDGE Share

Mainstream Polyester Production Processes

Polyester (such as PET chips and PBT) is one of the most widely used synthetic polymers in textiles, packaging, and engineering plastics. Its industrial production typically involves esterification/transesterification followed by polycondensation.



1. Direct Esterification Process (PTA Method)

Raw Materials: Purified Terephthalic Acid (PTA) + Ethylene Glycol (EG)

This is the most common method in PET production, where PTA reacts directly with EG to form bis(2-hydroxyethyl) terephthalate (BHET), which is then polycondensed into polyester resin.


Advantages:

Shorter process, lower energy consumption.

Lower cost compared with the DMT method.

High product purity and a narrow molecular weight distribution – ideal for polyester fiber and PET bottle chips.


Disadvantages:

Requires high temperature (250–290 °C) and pressure.

Demands high-purity PTA to prevent side reactions.


👉 Application: Over 90% of global PET fiber and bottle chip production adopts the PTA method.


2. Transesterification Process (DMT Method)

Raw Materials: Dimethyl Terephthalate (DMT) + Ethylene Glycol (EG)

This method first converts DMT and EG into BHET through transesterification, followed by polycondensation.


Advantages:

Milder reaction conditions (180–220 °C, atmospheric pressure).

DMT is stable and easy to store.


Disadvantages:

Generates methanol as a by-product, increasing environmental costs.

A more complex process with higher energy consumption.

Broader molecular weight distribution, leading to lower product performance.


👉 Application: Mostly replaced by the PTA process, but still used in PBT resin and some specialty polyester products.


3. Polycondensation Types in Polyester Production

(1) Melt Polycondensation

Conducted at 270–300 °C in the molten state under vacuum.

Pros: Continuous production, efficient, controllable intrinsic viscosity.

Cons: Thermal degradation risk, IV usually ≤ 0.72, high energy demand.

Application: Mainstream for PET bottle resin and polyester fiber chips.


(2) Solid-State Polycondensation (SSP)

Conducted in a solid state at temperatures below the melting point.

Pros: Produces high IV polyester (≥ 0.85), ideal for bottle-grade PET and industrial yarns.

Cons: Long processing time, high energy consumption, requires inert gas protection.


Bio-Based Polyester Production

Uses biomass-based EG or PTA (e.g., corn-derived EG). Hubei Decon can supply bio-based PET based on biomass-based EG. For more information,



source : Hubei Decon Polyester Co., Ltd

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